In the conventional spool type sizer or sizing machine, potatoes or other fruits or vegetables ride along a roll conveyor formed by a bed of spools or rollers all rotating in the same direction. The spacing between the rollers is adjusted for selectively passing and sorting the potatoes or other objects according to a size dimension. For elongate fruits, vegetables or other objects the selective sorting is based upon the short axis width or diameter. The spacing of the rollers is adjusted so that small diameter objects pass through the selective spaces between the rollers in a first section of the roll conveyor to a first bin or first receiving conveyor. The spacing between rollers is increased in the next section and the intermediate size objects fall into a second bin or on to a second receiving conveyor. Finally the larger size objects which do not pass through the selective spaces between rollers are carried along the top of the roll conveyor to a third bin or third receiving conveyor destination.
In some of the existing sizing machines, the rollers or spools rotate at stationary locations while in other existing devices the rollers or spools actually move along as a conveyor while also rotating. Spool-type roller conveyor structures are described for example in the Peterson U.S. Pat. No. 3,367,494. In the Peterson machine the selective spacing between rollers may be proportionally adjusted by means of a composite threaded shaft. Shaft sections of different pitch threads and different thread directions engage the respective roller mounts for maintaining equal or proportional spacing. The roller mounts slide on rails for variable spacing upon turning the shaft handle.
Spool type sizers with rolls all turning in the same direction may be obtained for example from the Better Built Potato Seed Cutter Company, 1649 West 3300 South Street, Salt Lake City, Ut 84119 and the Double L Manufacturing Co., American Falls, Id 83211. A variable spacing roller sizer for diameter grading in which the rollers expand in spacing as they advance along a conveyor for sorting by size is available from Kerian Machines, Inc., Highway 81 South, P.0. Box 311, Grafton, ND 58237.
In these rotating spool or roller sizing machines with rollers rotating in the same direction, separating and sorting of potato1s and similar objects takes place as the objects fall down and pass between a pair of rollers when the size dimension of the object corresponds to the spacing between the rollers. A disadvantage of this arrangement is that the potato or other object, typically a fruit or vegetable, always encounters an upward moving roller or spool surface on one side and a downward moving roller or spool surface on the other side. These counter moving surfaces of adjacent rollers produce a pinch effect which can bruise, damage or crush the fruits or vegetables in the process of sizing.